The present invention relates to a position detecting apparatus for electrically detecting the present position of a moving body reciprocated within a movable region.
Recently, a camera body and a photographing lens used for the camera have been greatly electronized or electrically operated. For example, with respect to the photographing lens, a group of lenses constituting this photographing lens are driven by a motor, etc., and can be set by the operation of a switch into a plurality of regions such as a variable power region in which the focal distance can be changed, a macro region for enabling a macro photographing, a housing region in which the lenses can be housed when they are not used.
To reduce the cost of a one chip micro computer (which is simply called "CPU" in the following description), the applicant of this application has considered and tried various kinds of experiments for performing, by the CPU, a control for changing the focal distance in the above variable power region, for example with respect to the photographing lens, especially, a control for performing the shift correction of a varifocal lens in which a shift in position of a formed image is caused by the change in focal distance.
It is possible to dispose the above CPU within the photographing lens to independently perform the control operation thereof. However, it is preferable that the photographing lens is also controlled by the CPU of the camera body from an economical view point. Accordingly, an operating switch operated by a user of the camera, a state detecting switch for detecting states of various kinds of mechanism portions of the camera body and the photographing lens, etc., are connected to input ports for recognizing an external state required to execute various kinds of controls by the CPU.
The number of input ports depends on the kind of the CPU but is limited, and it is desirable that the number of switches connected to the input ports is as small as possible to correspond to the extension of various kinds of control operations and the change in specifications of the camera and the photographing lens.
With respect to the photographing lens having the plural regions mentioned above, it is necessary to dispose a means for recognizing by the CPU in which region the above group of lenses are located. Concretely, it is considered to dispose a means for attaching a resistor onto a substrate and moving an electrically sliding brush on the resistor through the movement of the above group of lenses, and detecting the positions of the group of lenses by the change in resistance value.
However, the change in focal distance must be continuously detected within the above zoom region. On the other hand, in the macro and housing regions mentioned above, it is sufficient for the group of lenses to simply stop in a predetermined position so that it is not necessary to continuously detect the positions of the group of lenses. Accordingly, when one resistor is used to discriminate the above-mentioned three regions, the changing range of the resistance value of the resistor used in the variable power region is narrowed by an amount thereof used in the macro and housing regions. Therefore, the accuracy in detection of the focal distance, i.e., the accuracy in detecting the positions of the group of lenses in the variable power region is reduced.
To solve this problem, it is considered that a dedicated resistor be used in the variable power region and, in the macro and housing regions independent of the variable power region, several region discriminating patterns in the shape of a stripe composed of a combination of conductive and insulating sections are disposed in the shape of a flat face and the above brush is moved on the region discriminating patterns through the movement of the group of lenses to discriminate these regions by the combination of the above conductive and insulating sections. However, in the case of such a construction, it is necessary to dispose two substrates composed of a substrate for attaching thereto the brush and the resistor for the variable power region, and a substrate for disposing the region discriminating patterns and the brush for the housing and macro regions. Therefore, the two substrates are independent of each other and drive systems for the brushes are also independent of each other so that the accuracies in position detection thereof are reduced and the number of constructional members is increased, thereby increasing the number of adjusting operations.
Since the above members must be housed in a space limited within the camera, the area for the above substrates is limited and a space for disposing a lead portion for electrically connecting the above resistor or conductive section in such a condition must be further disposed. Correspondingly, the resistor and the conductive section are small-sized and the contact areas between these members and the brushes become small so that the operation of the apparatus becomes unstable.